Generally, a vehicle is provided with a passenger protecting system for protecting a passenger in a collision of the vehicle. The passenger protecting system has, for example, an airbag which is deployed in the collision to protect the passenger. It is desirable for the passenger protecting system to protect the passenger from not only the collision in the vehicle front-rear direction but also the collision (i.e., side-impact collision) in the vehicle lateral direction.
For example, referring to JP-B2-3011092 and JP-A-11-180249, the passenger protecting system for the vehicle has multiple sensors for detecting the collision and a determining unit for determining the collision with the vehicle based on signals from the sensors. When the determining unit determines that the collision occurs, a protecting unit such as the airbag and a pretensional will be actuated.
In this case, the sensors which are respectively mounted at different positions of the vehicle are connected with the determining unit, respectively via communication paths each of which is constructed of a communication wire and an interface circuit (I/F circuit). The communication paths are independent of each other. That is, the multiple sensors are connected with the determining unit in a one-to-one manner. In the case where there occurs an abnormality in one of the communication paths, a fluctuation due to the abnormality will be limited to the detection signal of the one sensor which is connected with this communication path.
However, in this case, when the number of the sensors is increased to improve the determining accuracy, the I/F circuit is to be added. Thus, the determining unit is big-sized so that the vehicle-mounted performance thereof is deteriorated.
Moreover, because the multiple sensors are connected with the determining unit respectively via the multiple wires, not only the wire number but also the whole wire length increases. Thus, the cost becomes high.
However, if the communication paths are bus-connected to collectively connect the multiple sensors with the determining unit, an abnormality in one of the communication paths will influence the detection signals of the multiple sensors which are connected with the one communication path. Thus, a faulty determination of the determining unit will be caused.